i have a 99 gixxer 600. the guy i bought it from put a 190 rear tire on and cahnged the sprocket. could the sprocket or larger tire cause my speedometer to give an incorrect speed. i ask because i was on the highway the other day with some friends. and since i knew how to get to where we were going i was up front. i thought i was doing about 80mph. but it seemed like cars were just wizzing by me. when we stopped i asked them how fast we were going and no one really payed any attention. any ideas?